Mobile vehicle comprising a friction clutch and an inch pedal

ABSTRACT

A mobile vehicle comprising a shiftable transmission with fixed gear ratio steps and a controllable friction clutch contains a distance sensor, which is connected to an inch pedal and in which the starting position and the end position of the inch pedal are adjusted by an electronic control unit and allocated to an inch effect from 0% to 100%. Due to the electronic adjusting process of the inch pedal path via the inch effect and the service brake, the intersecting time between the service brake and the actuating force of the clutch can be adjusted. The driving comfort of the vehicle is increased and the risk of damage to the multi-disk clutch is reduced.

The invention relates to a mobile vehicle comprising a shiftabletransmission, which contains at least one friction clutch in the drivetrain, wherein the friction clutch upon actuation of an inch pedal iscaused to slip in a targeted fashion so as to reduce the driving speedof the vehicle.

This shiftable transmission is especially necessary in machines, such aswheel loaders or high-lift trucks since in these vehicles low drivingspeeds are required when picking up loads, however, the operatinghydraulic system requires maximum power in this state. For this state,it is necessary to maintain the driving motor at the maximum possiblerotational speed in order to drive the hydraulic pump connected theretoat maximum rotational speed and to operate the friction clutch in aslipping manner, in order to reduce the driving speed. For this, theactuating force of the friction clutch can be lowered upon actuation ofthe inch pedal wherein, in the case of a minimal actuation path of theinch pedal, the actuating force of the friction clutch is reduced onlyslightly; the actuating force of the friction clutch is then furtherreduced during the continued actuation path of the inch pedal and beyonda defined actuation path of the inch pedal the service brake of thevehicle is additionally activated to further lower the driving speed.The friction clutch is exposed to the risk of damage in the slippingstate, especially when the frictional power exceeds a defined value.This can occur due to incorrect adjustment of the inch pedal and henceerroneous target values.

WO 00/22323 discloses a reversing gearbox that can be shifted under loadin which the pressure in the friction clutch is lowered in such a waythat by actuating a hydraulic inch valve said clutch changes into adefined slippage state. Especially hydraulic inch valves are verycomplex to adjust which, in conjunction with the hysteresis of saidhydraulic valve, leads to erroneous target values, and damage of thefriction clutch.

DE 198 30 950 A1 discloses a method and a device for actuating a motorvehicle clutch device in which a pedal position is used to generateappropriate voltage via a rotational angle sensor on the clutch pedal oron a separate inch pedal with said voltage being processed in anelectric control unit. By way of an inch pedal line, this voltage isconverted into the inch effect, which is between 0% and 100%. Thus it ispossible to cause the desired slippage for the reversing clutch. Inorder to protect the clutch from damage, the speed differential of theclutch device is modulated by varying the gear ratio in the inchoperation. However, this is only possible with continuously variablegear units and cannot be employed in powershift transmissions with fixedgear ratio steps.

It is the object of the present invention to create a mobile vehiclecomprising a shiftable transmission with fixed gear ratio steps and afriction clutch in which the friction clutch is brought into theslipping state in a targeted fashion and in which the friction clutch isprotected from damage.

The object is achieved with a generic mobile vehicle also comprising thecharacterizing features of the main claim.

A distance sensor is connected to the inch pedal, according to theinvention, and supplies an electric signal to an electric control as afunction of the pedal path, said control converting the signal into aninch pedal characteristic line, which is between 0% and 100%. 100% incheffect here means a disengaged friction clutch and 0% inch effect meansan engaged friction clutch. The electric signal is preferably voltage,which can be generated by a rotational angle sensor on the inch pedal.In order to avoid a complex adjustment of the distance sensor on theinch pedal, it suffices to mount the distance sensor on the inch pedalin such a way that the displacement path of the inch pedal is locatedwithin the displacement path of the distance sensor. In order to be ableto attribute the starting and ending signals of the distance sensor inthe electric control unit, the distance sensor is preferably adjustedelectronically when first starting up the vehicle. For this, theadjusting process is started via the electronic control unit, thereafterthe inch pedal is completely pushed down and is then returned slowlyinto the starting position. When moving the inch pedal back slowly, thevalued supplied by the distance sensor are preferably also measured inorder to exclude possible incorrect signals, e.g., caused by loosegears. The final positions of the inch pedal are then allocated in theelectronic control unit to the characteristic line 0% and 100% incheffect. This eliminates mechanical adjustment of the distance sensorentirely. Thus it is no longer possible that the friction clutch can bedamaged by incorrect adjustment of the distance sensor.

In another embodiment of the invention, the above-described system canbe used to easily attribute the maximum inch effect and, hence, theminimal actuating force of the clutch at which the clutch disks are juststarting to slip to a defined actuating state of the service brake. Byarranging the distance sensor for the inch function and the distancesensor for the service brake on one inch pedal and by using solely theinch function in a first path area and adding the service brake beyond adefined path area on the inch pedal, it is necessary to be able toallocate the pedal path exactly to the “inching” and “service brake”functions in the electronic control unit. Additionally, there is theproblem that the point at which the service brake is activated candiffer, depending on the customer's preferences. Erroneous settings maycause damage to the clutch.

In the arrangement of the distance sensor, according to the invention, asimple adjustment and setting of the service brake to the inchingfunction is possible. For this purpose, the vehicle is moved on analmost horizontal terrain. The adjusting process is started andpreferably a display prompts the operator to perform further actions.After the driving motor speed has been adjusted to a defined value,preferably the maximum rotational speed and the service brake has beenactuated, the process is started. By slowly releasing the service brake,the vehicle is set in motion. During this adjusting process, the clutchforce remains constantly adjusted within the inch effect 0% to 100%. Bypushing the inch pedal further down, the service brake is activated and,hence, the vehicle is slowed down. By measuring the vehicle motion, thebraking time is known from the pedal path of the inch pedal and isstored in the electronic control unit. The maximum inch effect, 100%, atwhich the disks of the friction brake just come into contact and whichcorresponds to a minimal actuating force of the clutch, is stored in theelectronic control unit as a function of the pedal path and can then bedetermined as described for example in WO 01/65227 A1 or in DE 198 26097 A1. Since now the electronic control unit has information about theminimal actuating force of the friction force and, hence, about thepoint 100% inch effect with the corresponding inch pedal position; theinch pedal position at which the service brake is activated, the servicebrake can now be programmed and thus set, by establishing thecharacteristic lines of the intersecting points of the inch, pressurewith the braking pressure.

In a further embodiment, the minimal decrease in the actuating force ofthe friction clutch is limited in such a way that the friction clutchduring the onset of inching and, hence, an inch effect greater than 0%,is not damaged even during extended operation of the clutch in theslipping state. Thus, during the onset of inching, the actuating forceof the clutch is reduced from the full actuating force to this definedactuating force, i.e., onset of inching. When pushing the inch pedaldown further, the actuating force is lowered further, however, this onlyfurther reduces also the frictional power and the friction clutch cannotbe damaged.

In a further embodiment of the invention, the electronic control unitdetects whether the inch pedal is moved in the “more inching” directionor whether the inch pedal is moved in the “less inching” direction.Since the inch function is preferably used in machines that can beoperated also on uneven terrain, it cannot be excluded that the driverperforms unintended movements on the inch pedal due to the uneventerrain. To ensure that the actuating force of the friction clutch doesnot change due to unintended movements of the inch pedal, a filtrationprocess is incorporated when changing the “more inching” function,therefore, a lower actuating force of the friction clutch and the “lessinching” function, thus, a higher actuating force of the friction clutchso that the “more inching” function switches to the “less inching”function only at a preset pedal path of the inch pedal. This presetminimum path, likewise, exists in the opposite direction.

In a further embodiment of the invention, especially in the case ofhydraulic actuating devices of the friction clutch, differentcharacteristic lines are used for the actuating pressure of theactuating device for the “more inching” functions, therefore, lessactuating pressure, and the “less inching” functions, accordingly moreactuating pressure. By using different characteristic lines for thesetwo functions, the hysteresis, which exists in the mechanical-hydraulicdrive and actuation of the friction clutch, and especially whenswitching from less actuating pressure to more actuating pressure andswitching in the opposite direction, can have no negative effects. Byeliminating said hysteresis through the use of different characteristiclines for the actuating directions, an immediate change in thetransmitted torque can be detected when changing the inch pedal path andthe pedal direction.

In another embodiment of the invention, the transition of these twocharacteristic lines is performed continuously when changing thedirection of motion of the inch pedal, thus eliminating any jerkyshifting in the vehicle. In another embodiment of the invention, thechange in the actuating force is limited above a defined actuating speedof the inch pedal, in order to prevent undesirable and unintendedshifting jolts, e.g., due to slippage from the inch pedal, therefore,the immediate return of the inch pedal. The change in the actuatingforce occurs continuously in such cases.

In another embodiment of the invention, the transition is effected viathe engaged clutch, accordingly the clutch with the maximum actuatingforce, to the onset of inching and, therefore, the minimal inch effectoccurs continuously, thus improving the driving behavior and minimizingthe load of the friction clutch. Likewise, the transition in theopposite direction occurs continuously.

In another embodiment of the invention, the frictional power iscalculated continuously from the time, the speed differential of theclutch and the actuating force of the clutch and, when a previouslydefined, permissible frictional power is exceeded, the actuating forceof the clutch is lowered, which can occur, for example, by lowering theclutch pressure, protecting the clutch from damage. Hence in a simplefashion, it is possible to use the “inching” function in the vehicle toadjust the distance sensor, to exclude erroneous actuation of the inchpedal, to prevent shifting jolts and damage to the clutch and thus toensure reliable operation in the vehicle.

Additional features are disclosed in the description of the figures.

The sole figure shows the course of an inch process across the pedalpath of the inch pedal.

The diagram is shown for a hydraulically actuated multi-disk clutch anda hydraulically actuated service brake. The multi-disk clutch and theservice brake are actuated by way of a hydraulic pressure in theengaging sense. The pressure for the hydraulic clutch and the hydraulicbrake is illustrated on the ordinate, the pedal path of the inch pedalon the abscissa. When the inch pedal is in its starting position 1,maximum pressure is applied to the friction clutch and hence it isengaged, which can be seen on line 2. The inch pedal is pushed down toan inching starting point 3 without changing the clutch pressure. Whenthe inch pedal is pushed down further than the inching starting point 3,the clutch pressure is lowered continuously to an inching start 4. Theinching start 4 clutch pressure has been previously defined and isdependent upon the power of the clutch at which the vehicle can beoperated with a slipping clutch over an extended period of time withoutdamaging the clutch. When pushing the inch pedal down further, theclutch pressure of the friction clutch decreases further until it hasreached a minimal clutch pressure 5 at which the disks of the clutchjust come into contact. Said clutch pressure can no longer be reducedfurther by the inch pedal. If now the inch pedal is moved back in theopposite direction, i.e., in the direction of the starting position,then the clutch pressure is immediately raised by a defined value, thusmaintaining the clutch actuating force, but causing the actuating deviceto actuate the clutch immediately in an engaging sense when increasingthe clutch force further due to a movement of the inch pedal in thedirection of the starting position since the hysteresis is compensatedby the use of an engaging characteristic line 7 due to the actuation ofthe components. By means of inching in the engaging sense on theengaging characteristic line 7 and in the disengaging sense on adisengaging characteristic line 6, the hysteresis of the components iseliminated, thus passing on immediate responsive behavior of the inchfunction to the driver. Erroneous operation by the driver, due to aninch pedal that has been pushed down or released too far, therefore, iseliminated. When the inch pedal reaches a motion point 8, the servicebrake is also activated, which can be seen from line 9. When theengaging characteristic line 7 reaches a point 10, which is, likewise,defined such that the friction clutch is not damaged during extendedoperation and the inch pedal is moved further in the direction of thestarting position, the clutch pressure is increased continuously up tothe maximum clutch pressure thus completely engaging the clutch. Whenthe clutch is operated for an impermissibly long time in a slippingstate, the clutch is automatically actuated in the disengaging sense.The inch pedal must be pushed down further to start the inch processthan when leaving the inch process. The difference between the inchingstarting point 3 and an inching end point 11 causes a brief erroneousoperation of the gas pedal to have no negative effect when driving onuneven terrain. Through the electronic adjustment of the distance sensorand the detection of a starting point 12 of the service brake, it ispossible to adjust the inch function as desired with the characteristicline of the service brake 9 in the electronic control system, thusactivating the service brake earlier or later, depending on theprogramming.

REFERENCE NUMERALS

-   1 starting position-   2 line-   3 inching starting point-   4 onset of inching-   5 minimal clutch pressure-   6 disengaging characteristic line-   7 engaging characteristic line-   8 motion point-   9 line-   10 point-   11 inching end point-   12 starting point

1-4. (canceled)
 5. A mobile vehicle comprising a shiftable transmissionwith fixed gear ratio steps, which contains a friction clutch that canbe engaged by an actuating force, an inch pedal, a pedal path of whichis detected by a distance sensor, and supplied to an electronic controlunit, upon actuation of the inch pedal, the electronic control unitlowers the actuating force of the friction clutch as a function of thepedal path and then brings the friction clutch into a slipping state,the pedal path of the inch pedal is located within a motion path of thedistance sensor, and a starting position and an end position of the inchpedal are detected by the electronic control device, and allocated to aninch characteristic line, the starting position and the end position ofthe inch pedal are allocated to the characteristic line of a 0% and 100%inch effect by adjusting the distance sensor electronically.
 6. Themobile vehicle comprising a shiftable transmission according to claim 5,wherein the inch characteristic line has an inch effect of 0% to 100%.7. The mobile vehicle comprising a shiftable transmission according toclaim 5, wherein an intersecting point of the inch characteristic lineto a service brake characteristic line can be adjusted.
 8. The mobilevehicle comprising a shiftable transmission according to claim 5,wherein the electronic control unit detects the inch pedal path, atwhich a service brake is activated, by means of which the vehicle isdelayed, recognized by measuring a motion change of the vehicle, andstored.